1. Field of the Invention
The present invention pertains to hydraulic spike pullers or pulling tools.
2. Discussion of Related Art
Spike pullers are devices used to remove rail fasteners commonly called rail spikes. Currently, there exist numerous spike pullers in the market. In the present description, the term “spike puller” refers to a device that is capable of removing, extracting or pulling a rail spike.
FIG. 1 shows a cross-sectional view of a conventional hydraulic spike puller 10 manufactured by Stanley Black and Decker, commonly referred to as Stanley Hydraulic Tool (SHT). SHT 10 has an upper body portion 11A and a lower body portion 11B. The upper portion 11A includes a housing (e.g., cylinder) 12. The cylinder 12 includes a tubular portion 13 capped by head portion 12A and bottom portion 12B. SHT 10 also includes piston 14 configured to axially move within the cylinder 12. Fixed to the underside of piston 14 is piston rod 16. A first end 16A of piston rod 16 is connected to piston 14. A second end 16B of piston rod 16 is connected to spike puller jaw assembly 18 which includes articulated jaws 18A and 18B. Piston rod 16 has a hollow axial bore 17 extending along most of a length of piston rod 16. Piston rod 16 is axially slideable within lower body portion 11B.
SHT 10 further includes fixed hollow tube 20. Fixed hollow tube 20 is connected to cylinder head 12A and extends axially from the cylinder head 12A through piston 14 into piston rod 16. Fixed hollow tube 20 extends the length of cylinder 13 into hollow axial bore 17 of piston rod 16. The external diameter of fixed hollow tube 20 is smaller than the internal diameter of hollow axial bore 17.
SHT 10 further includes hydraulic valve assembly 22 disposed adjacent cylinder head 12A. Hydraulic valve assembly 22 is configured to be manually operated by trigger 24 to direct hydraulic fluid pressure either to the top 14A of the piston 14 so as to extend the piston rod 16 or to the underside 14B of piston 14 so as to retract the piston rod 16 and pull the spike (not shown) using spike puller jaw assembly 18.
In operation, when raising the piston to pull a spike, the valve assembly 22 directs hydraulic fluid down through the axial fixed hollow tube 20 so as to direct hydraulic fluid to the underside 14B of the piston 14. The hydraulic fluid exits the open end of the fixed hollow tube 20, and fills and pressurizes bore 17 of piston rod 16. The hydraulic fluid moves axially upward through a space between an external surface (external diameter) of the fixed hollow tube 20 and an internal surface (internal diameter) of the bore 17.
At a position proximate to the underside 14B of piston 14, the piston rod 16 includes a number of radial ports 26 extending through a wall of the piston rod 16. The oil moves radially outward through the ports 26 and underneath the piston 14, causing the piston 14 to rise upward within cylinder 12.
As will be explained in the following paragraphs, it is desirable to raise piston 14, i.e., raise or retract piston rod 16, at a first slower speed and then, after it has moved a first axial distance, to continue raising or retracting piston 14 and piston rod 16 at a second faster speed. In SHT 10, this is performed manually, by manually actuating trigger 24 to actuate hydraulic valve assembly 22 to a first position and then to a second position.
In the first position, only part of the hydraulic fluid and pressure is directed axially down the fixed tube 20, while another part of the hydraulic fluid pressure is bled off via a relief valve 28 back to the hydraulic return line (not shown). The reduced flow or partial pressure of the hydraulic fluid, generated when the valve assembly 22 is at the first position, yields the first slower rise or retraction speed of piston 14 or piston rod 16.
In the second position, the relief valve 28 is blocked and no bleeding of hydraulic fluid flow or hydraulic fluid pressure occurs. As a result, full hydraulic pressure and hydraulic flow are directed down the fixed tube 20 to the underside of piston 14B which yields the second faster rise or retraction speed of piston 14 and piston rod 16.
Hence, the rise or retraction of piston 14 or piston rod 16 is performed in two stages, a first slower speed stage and a second faster speed stage. As the piston rod 16 retracts, the jaws 18A and 18B in jaw assembly 18 pivot and grip or clamp the head of the spike or workpiece (not shown) to be pulled. This clamping or gripping clamping action tends to seat or pull the SHT 10 into axially alignment with the spike (not shown). In some instances, it may be desired to have an initial movement of clamping and aligning of the SHT 10 at a slower speed. Once the spike is clamped by the jaws 18A and 18B of jaw assembly 18 and SHT 10 has self-aligned, the user may then be able to pull the spike quickly with a second faster raising of piston 14 and piston rod 16.
Even though conventional SHT 10 provides dual stage or dual retraction speed of the piston 14 and piston rod 16, the operation of controlling the speed of retraction of piston 14 and piston rod 16 to achieve the dual retraction speed is performed manually by controlling the operation of the head valve 22 using trigger 24. Hence, it is desirable to provide for automatic two step or dual speed operation of the pulling or retracting process.
FIG. 2 is a cross-sectional view of another conventional spike puller 30. Spike puller 30 is manufactured by Geismar Corporation, France. Spike puller 30 also operates in a dual retraction speed mode. Spike puller 30 achieves the dual retraction speed automatically. Spike puller 30 includes a piston rod 32, a piston 34 connected to the piston rod 32, and a cylinder 36 housing both the piston rod 32 and piston 34. Hydraulic fluid (oil) is directed to underside 34A of piston 34 via oil line 38 located external to the cylinder 36. External oil line 38 has two branches 38A and 38B that enter the cylinder 36 via an upper radial port 36A and a lower radial port 36B, respectively. Lower radial port 36B is located below the piston 34 when the piston is in its start position. Upper radial port 36A is located at a height corresponding to the predetermined height at which it is desired to transition to high speed retraction.
Until the piston 34 rises above the level of port 36A, radial port 36A which is connected oil line 38A is blocked and oil flows to the underside 34A of piston 34 only via lower port 36B which is connected to oil line 38B. Lower port 36B has a check valve 39. Check valve 39 admits oil at restricted speed and pressure via its orifice 39A during retraction of piston 34. However, when the piston 34 rises above the position of port 36A, full oil flow and pressure is provided via oil line 38A to the underside 34A of piston 34. As a result, piston 34 continues to rise, but at a second faster speed. Thus, the spike puller 30 provides automatic transition from slow initial or first retraction to faster later or second retraction after a predetermined movement of the piston 34.
Similarly, during lowering or resetting of the spike puller 30, the underside of the piston 34A is initially vented via port 36A connected to oil line 38A, and descent of the piston 34 is relatively fast. However, when the descending piston 34 reaches the position of port 36B, piston 34 blocks port 36B. As a result, the pressure for evacuating oil through port 36B, oil line 38B and through check valve 39 increases. The increased oil pressure unseats check valve 39 and moves check valve 39 away from the external oil line 38. Hence, the speed of descent is maintained relatively fast during the lowering or resetting of piston 34.
Although spike puller 30 achieves the dual retraction speed automatically, the dual retraction speed is achieved by the use of external line 38 and check valve 39 which adds complexity to the overall spike puller 30. In addition, the use of external line 38 and check valve 39 may render the spike puller 30 vulnerable to damage.
As it can be appreciated from the above paragraphs, conventional spike pullers have certain drawbacks and limitations. A spike puller according to various embodiments of the invention, as described in the following paragraphs, circumvents the drawbacks of conventional spike pullers.